1. Field of the Invention
The present invention relates to a process for preparing a thin film having alternating monolayers of a metal-metal bonded complex monolayer and an organic monolayer by layer-by-layer growth. More particularly, the present invention relates to a thin film having alternating monolayers of a metal-metal bonded complex monolayer and an organic monolayer.
2. Description of the Prior Art
During the past three decades, considerable progress has been made in the understanding of dinuclear compounds containing multiple metal-metal bonds. Both the experimental and the theoretical aspects of these compounds have been explored extensively. These studies have provided a large body of information particularly in the following areas: the reactivities of the dinuclear cores, the strengths of metal-metal interactions, the electronic transitions between metal-based orbitals and those involving metal to ligand charge transfer, the redox activities of the dinuclear core, and the correlation among these properties (See, e.g., Cotton, Walton, Multiple Bonds Between Metal Atoms, 2nd Ed., Oxford, 1993).
Efforts focusing on technologically important applications of dinuclear compounds have led to many promising research areas, such as inorganic liquid crystals (See, e.g., Chisholm, Acc. Chem. Res., 2000, 33, 53), antitumor agents (See, e.g., Hall, et al, J. Clin. Hematol. Oncol., 1980, 10, 25), and homogeneous and photolytic catalysis (See, e.g., Doyle, Aldrichimica Acta, 1996, 29, 3; Nocera, Acc. Chem. Res., 1995, 28, 209).
Layer-by-layer assembly techniques to fabricate multicomponent films has been explored in the literature. One of the most developed systems grown layer-by-layer is the layered metal phosphates and phosphonates. The films include multivalent metal ions, e.g. Zr4+, and organic molecules terminated with an acidic functionality, e.g. a phosphonic acid (See, e.g., Cao, Hong, Mallouk, Acc. Chem. Res., 1992, 25, 420). Katz and co-workers have used this method to align hyperpolarizable molecules into polar multilayer films that show second-order nonlinear optical effects (See, e.g., U.S. Pat. Nos. 5,217,792 and 5,326,626). A similar approach has also been extended to other materials such as polymers, natural proteins, colloids, and inorganic clusters (See, e.g., Decher, Science, 1997, 277, 1232). This same technique has also been applied to the production of other multilayers including Co-diisocyanide, dithiols with Cu, and pyrazines with Ru (See, e.g., Page, Langmuir, 2000, 16, 1172).
Among the existing examples, the driving force for the film progression is mainly the electrostatical interaction between polycations and polyanions; few examples involve other types of interactions, such as hydrogen bond, covalent, or mixed covalent-ionic. The present invention utilizes strong covalent interactions, rather than ionic interactions, between the metals and the ligands in a novel strategy to assemble nearly perfectly packed mutilayers.
Despite the abundance of activity, efforts so far have been limited to the study and use of the metal-metal bonded compounds in solution-based systems. To harness the electronic, optical, and magnetic properties of metal-metal bonded materials in solid-state applications and devices, development of new methods for making thin films containing functional metal-metal bonded complexes are needed.
Accordingly, the present invention provides methods to grow multilayer thin films including metal-metal bonded compounds.